Chapter 4 Analog Input
© National Instruments Corporation 4-37 NI USB-621x User Manual
The differential connection configuration allows the common-mode noise
voltage, V
cm
, to be rejected during the measurement of V
1
.
You must connect the negative lead of your sensors and AI GND to a local
ground signal on your system.
Taking Referenced Single-Ended (RSE) Measurements
Using the RSE measurement configuration allows the
USB-6215/6216/6218 to take measurements on all AI channels when all
channels share a common ground. Figure 4-25 shows an RSE connection
configuration.
Note If you leave the AI GND pin unconnected, the signals float outside the working input
range of the USB-6215/6216/6218. This can result in unreliable measurements because
you cannot ensure that the input signal is within 10 V of AI GND.
Figure 4-25. Connecting to the USB-6215/6216/6218 in RSE Mode
In an RSE connection configuration, each input channel is measured with
respect to AI GND.
AI 1
AI 2
AI GND
USB-6215/6216/6218
Mux
ADCPGIA
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